Optimum Design of Lay-Up Configuration and Ply Drop-Off Placement for Tapered Composite Laminate

The present study optimizes lay-up configurations and drop-off placements to maximize the failure strength of tapered laminates. A lookup table of stress components for calculation of Christensen’s criteria is prepared in advance for all possible combinations of 3-ply laminates which is the minimum structure of ply dropoff. Stress components at three corners of resin pockets modeled triangular are first obtained from the finite element analysis (FEA). Then, the optimization is conducted for the laminate which tapers from 16- to 8-ply by using a simple genetic algorithm method. Objective functions are evaluated by referring only stress indexes listed in the lookup table and the FEA are not performed during the optimization. Both thick and thin sections are limited to quasi-isotropic laminates with 45° increment angle, but a stacking sequence of plies is variable and optimized. Placement of ply drop-off are also design variables. It was revealed that 0° and 90° plies are dropped near the thick and thin sections for the optimum result. Experimental results validated that the optimum structure has higher failure strength than the reference one.